title: Early changes in brush border disaccharidase kinetics in rat jejunum following subcutaneous administration of tetraiodothyronine: a quantitative histochemical study on villi revealing normal morphology.
abstract: In order to test the influence of thyroid hormones on small intestine function, adult female Wistar rats were injected daily with either 100 microgram/100 g body weight tetraiodothyronine or placebo. After 12 days, jejunal segments were removed and processed for morphometric analysis of mucosal architecture and quantitative histochemical determinations of the apparent Km- and Vmax-values of lactase/beta-glucosidase and neutral alpha-glucosidase at constant basal and apical measuring positions along the villi. The villus-crypt-architecture was the same in both experimental groups. At the cellular level, however, application of tetraiodothyronine resulted in a marked decrease in the apparent Vmax of lactase/beta-glucosidase at both villus positions, maintaining the normal activity gradient along the villi. In comparison with the controls, a less pronounced but significant reduction in activity was also demonstrated for the neutral alpha-glucosidase. Substrate affinity, however, was only increased for this enzyme, the apparent Km of lactase/beta-glucosidase not being affected by the hormone. The results indicate a direct effect of tetraiodothyronine on jejunal brush border disaccharidases of the rat. The alternative mechanism, an effect mediated by an altered enterocyte turnover is unlikely to occur.
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000187:drug effects*; D004186:Disaccharidases / Q000037:antagonists & inhibitors*; D005260:Female; D006651:Histocytochemistry; D007583:Jejunum / Q000187:drug effects* / Q000201:enzymology; D008871:Microvilli / Q000187:drug effects* / Q000201:enzymology; D051381:Rats; D011919:Rats, Inbred Strains; D013974:Thyroxine / Q000494:pharmacology*; D001616:beta-Galactosidase / Q000037:antagonists & inhibitors; D001617:beta-Glucosidase / Q000037:antagonists & inhibitors
chemical_list: D004186:Disaccharidases; D001617:beta-Glucosidase; D001616:beta-Galactosidase; D013974:Thyroxine